Suppose such an organism had evolved from using sound like most life we know to use different intensities, wave lengths, and hues of light to communicate.

This is assuming that these creatures are as or more intelligent as humans currently and emit the light themselves from their face, these organisms are humanoid.

What effect would such a change have on the rest of their physiology?

  • $\begingroup$ Are you asking specifically about language, rather than the broader meaning of communication? You will get more specific answers the more specific your question is. $\endgroup$ – trichoplax Oct 16 '14 at 22:00
  • $\begingroup$ I would expect that where they emit the light from would have an effect on their subsequent evolution. For example, emitting light from the entire skin surface will allow communication over greater distance but will require more energy. This may also affect the subsequent evolution of the eye, or potentially separate light sensors specifically for this form of communication. $\endgroup$ – trichoplax Oct 16 '14 at 22:05
  • $\begingroup$ In the strictest sense, sign-language uses light to communicate. But since you're looking for emitted light rather than reflected light, I think the term you're looking for is bioluminescence. You might want to update your title. $\endgroup$ – Caleb Hines Oct 16 '14 at 22:09
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    $\begingroup$ Research the Humboldt squid if you want to see the practice of bioluminescence communication in Earth terms. $\endgroup$ – Twelfth Oct 16 '14 at 23:33
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    $\begingroup$ Fireflies. Humboldt squid. I think Mantis shrimp as well. Surely the only crucial physiological developments are those necessary to control the luminescence as well as we control our vocal cords. $\endgroup$ – CAgrippa Oct 17 '14 at 0:01

The first and most obvious requirement is that they would need light sensitivity, so vision is a must.

Beyond that there are some differences between the way light and sound work, for example hearing is 360 degree coverage, if someone shouts behind you then you can still see it. Equally sound can be used for communication around corners or over hills.

As a result light is actually quite weak to use as an early warning signal, so it is likely that there would be some auditory communication as well even if it's restricted to alarm and distress signals.

One advantage of visual signalling is the available bandwidth, if you had a creature with the ability to change its skin dramatically and rapidly in various patterns and shapes then it could well be able to transmit information far faster and at longer ranges than speech.

Multiple creatures could all be "speaking" in the same area at the same time without interference and conversations would not need people to wait for each person to finish. Instead even in a multi-way conversation each person could constantly talk all the time, so expect them to be better at multi-tasking and processing multiple information streams simultaneously than humans are. In general their visual processing would be superior to humans but their auditory processing would be weaker.

Technology would take different routes from our own, as the telephone and radio would both be pointless. Early remote communication would most likely be something like the telegraph and writing could well be hieroglyphics designed to look like the skin patterns used to "speak".

They may well develop independently mobile eyes so that they can watch people they are talking to at the same time as working. For example a conversation while sewing would require two eyes to watch the sewing process and another to watch the conversation. A group conversation may require either one eye on each person in the conversation or some sort of signal that causes everyone to switch attention to the person who is going to speak.

  • $\begingroup$ I imagine their eyes are going to by much more like a fly's compound eyes to get a wide area of vision. $\endgroup$ – Liath Oct 20 '14 at 15:05

We already have animals that communicate by light. The one most people have seen are lightening bugs. Granted it's mostly for 'lets propagate' but it is a form of communication. There are plenty of animals in the deep that use light for different things.

However, the closest and most intelligent animal that uses light is the octopus (and it's cousin the cuttlefish). They use their chromatophores for quite a few different things. They will use it as camouflage, but it can also be used to threaten predators, mesmerize prey, and attract a mate. The cuttlefish have some absolutely amazing displays that are very incredible. They can even appear to be trying to communicate with divers.

So I would think the cephalopods are a good place to start for ideas of light as communication. At least as primary communication, as someone pointed out, sound would likely still needed to be used for warnings and such, but the bandwidth of the light could be much, much higher allowing for a much more exact transfer of information between individuals.


If light was the dominate form of communication then I would expect the physiology to reflect the dependence on light. Unlike us they may have additional "eyes" that allow them to receive messages from other directions. Think like the compound eyes on most insects or an arachnids multiple (6-8) eyes that form a photo sensitive "wreath" around their heads. Eye stalks might be another option, rather then a single directional approach like our eyes take maybe a complex compound eye sits atop a couple of eye stalks (much like long rabbit ears or antenna).

The other thing to consider might be what what range of light for them is visual and which is "auditory" can they see the same wavelengths we do? If so they may then use a more invisible (to us anyway) light wavelength for communication like infrared or x-ray.

This gives such a species some interesting angles for making communication difficult; perhaps the "speech" wavelength is just plain red so this species is effectively red color blind and is very confused by some of our lights. The flip side to this is that using a wavelength in the x-ray spectrum may cause damage to species less able to deal with the "radiation" of their speech.


This is not an exact answer like the others. But, if there exists such a creature, everything around them will produce "sounds" in terms of light and they probably will name objects according to their colors. The ambient color would affect their mood and psychology.

It is also possible to use lower frequency electromagnetic waves (since visible light is as such but at a very high frequency). Lower frequencies can be used to communicate longer distances and would be broadcasted to a larger area (like radio signals). This would allow them to communicate long distance without any equipments.


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